WO2005109556A1

WO2005109556A1 - Fuel cell and separator thereof

Info

Publication number: WO2005109556A1
Application number: PCT/IB2005/001254
Authority: WO
Inventors: Seiji Mizuno
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2004-05-11
Filing date: 2005-05-10
Publication date: 2005-11-17
Also published as: JP2005322595A

Abstract

In a fuel cell, a plurality of supply gas passages (6a, 7a) and a plurality of discharge gas passages (6b, 7b) are formed in a separator. Communication between the supply gas passages and the discharge gas passages is not permitted. In the thus configured fuel cell, a member (2) of the separator, which forms portions between the gas passages is porous. Thus, water generated at electrodes (3, 4) can be absorbed in the porous members (2). It is therefore possible to suppress occurrence of blockage in the catalytic layer and the diffusion layer due to water existing at the electrodes (3, 4). Namely, flooding can be prevented. As a result, it is possible to increase an area in the fuel cell, where a reaction actually occurs, and therefore increase a power density of the fuel cell.

Description

FUEL CELL AND SEPARATOR THEREOF

FIELD OF THE INVENTION [0001] The invention relates to a cell structure of a fuel cell.

BACKGROUND OF THE INVENTION [0002] In order to improve performance of a fuel cell, for example, a structure of the fuel cell have been developed in various methods such that gas can be supplied to a catalytic layer of the fuel cell further efficiently and water generated due to a reaction of oxygen and hydrogen can be discharged further efficiently. For example, if the gas does not diffuse sufficiently in a region in the fuel cell, in which gas passages formed in a separator contact an electrode, efficient electric power generation using the entire electrode cannot be performed. Therefore, in order to solve this problem, various proposals have been made on structures and shapes of a gas supply passage and a gas discharge passage. [0003] For example, Japanese Patent Application Publication No. JP(A) 11 -16591 discloses a fuel cell in which a closed passage structure is applied to each of a supply gas passage and a discharge gas passage. More particularly, in the fuel cell disclosed in Japanese Patent Application Publication No. JP(A) 11-16591, the supply gas passage and the discharge gas passage formed in a separator are separated from each other, and the communication between the supply gas passage and the discharge gas passage is not permitted. Japanese Patent Application Publication No. JP(A) 07-45294 discloses a fuel cell in which a porous passage structure is applied to a gas passage. More particularly, in the fuel cell disclosed in Japanese Patent Application Publication No. JP(A) 07-45294, gas passages are formed by arranging multiple porous current collector small pieces between a platy separator and an electrode base plate. [0004] However, in the fuel cell disclosed in Japanese Patent Application Publication No. JP(A) 11-16591, if an amount of water existing in a catalytic layer and a diffusion layer becomes large with respect to a gas flow speed, the water cannot be sufficiently discharged to the discharge gas passages, and therefore a blockage due to the water occurs in the catalytic layer and the diffusion layer. Also, in the fuel cell disclosed in Japanese Patent Application Publication No. JP(A) 07-45294, the water is accumulated non- uniformly in the cell, and therefore an area in the fuel cell, where a reaction actually occurs is reduced. DISCLOSURE OF THE INVENTION [0005] It is an object of the invention to provide a fuel cell whose gas diffusion region is increased and whose performance of discharging generated water is improved, and a separator thereof. [0006] A first aspect of the invention relates to a fuel cell in which communication is not permitted between a supply gas passage and a discharge gas passage that are formed in a separator provided on an electrode. In this fuel cell, a member of the separator, which forms a portion between the supply gas passage and the discharge gas passage is porous. [0007] In the above-mentioned fuel cell, a plurality of the supply fuel gas passages (hereinafter, referred to as "gas passages" where appropriate) through which supplied gas flows and a plurality of the discharge gas passages (hereinafter, referred to as "gas passages" where appropriate) through which discharged gas flows are formed in the separator. Communication between the supply gas passages and the discharge gas passages is not permitted. Namely, the gas passages are not connected with each other. The separator is provided on each of the electrodes (anode and cathode). In the fuel cell having such a structure, the member of the separator, which forms the portion between the gas passages is porous. Therefore, the water generated due to electric power generation at the electrode can be absorbed by the porous member. Accordingly, it is possible to suppress occurrence of blockage in the catalytic layer and the diffusion layer due to the water existing at the electrode. Namely, flooding can be prevented. As a result, it is possible to increase an area in the fuel cell, where a reaction actually occurs, and therefore increase a power density of the fuel cell. [0008] In the above-mentioned fuel cell, the diffusion layer of the electrode may be porous, and the porosity of the member may be higher than the porosity of the diffusion layer. Namely, the gas permeation resistance of the member of the separator is made lower than the gas diffusion resistance of the diffusion layer. Thus, the reaction gas can move from the supply gas passage to the discharge gas passage more efficiently. As a result, it is possible to increase the amount of water absorbed in the porous member. [0009] In the above-mentioned fuel cell, the member may be configured such that the porosity thereof increases toward the downstream side in the gas flow. Namely, the gas permeation resistance of the member positioned on the downstream side in the gas flow is made small. Thus, the generated water, which is likely to be accumulated on the downstream side in the gas flow as compared to on the upstream side in the gas flow, can be reliably absorbed in the porous member. As a result, it is possible to discharge the generated water efficiently. [0010] In the above-mentioned fuel cell, the member may be provided in only the separator on the cathode side of the fuel cell. The porous member is not applied to the member on the anode side of the fuel cell, and only the member on the cathode side is porous. If the portion between the gas passages is formed of the porous member, the supplied gas is discharged unnecessarily. Therefore, the porous member is not used on the anode side where hydrogen serving as fuel flows. Water is generated mainly on the cathode side. Accordingly, even when the porous member is used on only the cathode side, the generated water can be discharged sufficiently. [0011] In the above-mentioned fuel cell, the porosity of the member on the cathode side may be higher than the porosity of the member on the anode side. It is therefore possible to appropriately discharge the water on the anode side while suppressing unnecessary discharge of the hydrogen on the anode side. [0012] A second aspect of the invention relates to a separator for a fuel cell, in which a supply gas passage and a discharge gas passage are formed such that communication between the supply gas passage and the discharge gas passage is not permitted. In this separator, a member of the separator, which forms a portion between the supply gas passage and the discharge gas passage is porous. BRIEF DESCRIPTION OF THE DRAWINGS [0013] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: FIG. 1 is a perspective view schematically showing a structure of a fuel cell according to an embodiment of the invention; FIG. 2 is an enlarged view showing a region A 1 indicated by a dashed line in FIG. 1 ; FIG. 3 is a plan view of the fuel cell viewed from a direction indicated by an arrow A2 in FIG. 1; FIG. 4 is a cross sectional view showing a diffusion layer and a porous body according to the embodiment; FIG. 5 is a cross sectional view showing the porous body with a supply gas passage according to the embodiment formed therein; FIG. 6 is a view showing a cell to which a structure of a separator and a porous body according to a first modified example is applied; FIG. 7 is a view showing a cell to which a structure of a separator and a porous body according to a second modified example is applied; and FIG. 8 is a graph showing a current-voltage characteristic of the fuel cell according to the embodiment and current-voltage characteristics of known fuel cells.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0014] Hereinafter, a preferred embodiment of the invention will be described with reference to accompanying drawings. [0015] [Structure of Fuel Cell] FIG. 1 is a perspective view schematically showing a structure of a fuel cell 100 according to an embodiment of the invention. As shown in FIG. 1 , the fuel cell 100 is formed by stacking multiple cells 50 (hereinafter, the cell 50 will be referred to as a "fuel cell" where appropriate). The fuel cell 100 is mounted in, for example, a fuel cell vehicle (hereinafter, simply referred to as a "vehicle"), and drives the vehicle using electric power generated therein. [0016] A structure of the cell 50 will be described in detail with reference to FIG. 2. FIG. 2 is an enlarged cross sectional view showing a region Al indicated by a dashed line in FIG. 1. FIG. 2 is the cross sectional view of the cell 50 taken along a surface peφendicular to a direction in which gas passages extend. The cell 50 includes separators 1 , porous bodies 2, diffusion layers 3, catalytic layers 4, an electrolyte membrane 5, supply gas passages 6a and 7a, and discharge gas passages 6b and 7b. In FIG. 2, the upside is the anode side, and the downside is the cathode side. [0017] In the cell 50, the anode and the cathode are formed with the electrolyte membrane 5 inteφosed therebetween. On each of the anode side and the cathode side, the catalytic layer 4 is formed on the electrolyte membrane 5, and the diffusion layer 3 is formed on the catalytic layer 4. The supply gas passage 6a and the discharge gas passage 6b are formed on the diffusion layer 3 on the anode side. Also, the supply gas passage 7a and the discharge gas passage 7b are formed on the diffusion layer 3 on the cathode side. Hereafter, these gas passages will be collectively referred to as the "gas passages" where appropriate. Anode gas (hydrogen) supplied from the outside of the cell 50 flows through the supply gas passage 6a on the anode side. Cathode gas (oxygen) supplied from the outside of the cell 50 flows through the supply gas passage 7a on the cathode side. Also, the gas discharged from the anode flows through the discharge gas passage 6b on the anode side. The gas discharged from the cathode flows through the discharge gas passage 7b on the cathode side. On each of the anode side and the cathode side, the porous body 2 is provided between the gas passages and above the gas passages, and the separator 1 is provided on the porous body 2. [0018] The separator 1 is formed of a flat plate. The separator 1 collects electrons generated by a reaction of hydrogen and oxygen, and has good electrical conductivity as an electric connector located between the adjacent cells. In addition, the separator 1 has corrosion resistance to the slightly acidic electrolyte membrane 5. Also, the separator 1 separates the adjacent cells 50 when the cells 50 are stacked, and also separates oxygen from hydrogen. [0019] The porous body 2 has ribs 2R. Namely, a space surrounded by a main portion of the porous body 2, the ribs 2R of the porous body 2 and the diffusion layer 3 forms the gas passage. In the porous body 2 on the anode side, the supply gas passages 6a and the discharge gas passages 6b are formed alternately in a direction perpendicular to the direction in which these gas passages extend. Also, in the porous body 2 on the cathode side, the supply gas passages 7a and the discharge gas passages 7b are formed alternately in the direction peφendicular to the direction in which these gas passages extend. The porous body 2 is made of a porous material, and has multiple holes therein. Accordingly, the porous body 2 can retain fluid (e.g., gas and liquid) in the holes. [0020] The diffusion layer 3 is formed on the catalytic layer 4. The diffusion layer 3 is used for uniformly diffusing the gas on the electrolyte membrane 5. The diffusion layer 3 is also made of a porous material. The diffusion layer 3 has not only electrical conductivity but also water repellency. [0021] The catalytic layer 4 is formed on the surface of the electrolyte membrane 5. The catalytic layer 4 ionizes the adsorbed gas (e.g., hydrogen gas). Namely, the catalytic layer 4 extracts ions from the hydrogen. The electrolyte membrane 5 is formed of, for example, a polymer electrolyte membrane which permits only hydrogen ions to permeates therethrough. [0022] Next, how the gas flows in the cell 50 will be described. First, the gas flow will be roughly described. The hydrogen flowing through the supply gas passage 6a on the anode side reaches the catalytic layer 4 while being diffused in the diffusion layer 3 as shown by arrows 10a. Then, hydrogen ions are extracted in the catalytic layer 4, and taken into the electrolyte membrane 5. The hydrogen gas, which is not taken into the electrolyte membrane 5 at this time, flows through the discharge gas passage 6b. Meanwhile, the oxygen flowing through the discharge gas passage 7b on the cathode side reaches the catalytic layer 4 while being diffused in the diffusion layer 3 as shown by arrows 10b. Then, in the catalytic layer 4 on the cathode side, the hydrogen ions supplied from the anode side react with oxygen, and therefore water is generated. Also, electrons move from the anode to the cathode through a load located outside of the fuel cell 100. The gas flowing through the discharge gas passages 6b and the gas flowing through 7b (containing unused hydrogen and oxygen) are also taken into the electrolyte membrane 5, and used for generating electric power. [0023] In the embodiment, the portions between the gas passages are formed of the porous body 2. Accordingly, as shown by an arrow 2a, part of the gas in the supply gas passage 6a permeates through the rib 2R of the porous body 2, and moves to the discharge gas passage 6b. Similarly, part of the gas in the supply gas passage 7a permeates through the rib 2R of the porous body 2, and moves to the discharge gas passage 7b. Namely, part of the gas in the supply gas passages 6a and part of the gas in the supply gas passage 7a move to the discharge gas passages 6b and 7b, respectively, without moving through the diffusion layers 3. Due to this gas movement, a negative pressure is generated in each of the supply gas passages 6a and 7a. Due to this negative pressure, the water existing in the diffusion layer 3 and the catalytic layer 4 can be absorbed in the porous body 2, as shown by arrows 11 on each of the anode side and the cathode side. It is therefore possible to suppress occurrence of blockage due to the water existing in the diffusion layer 3 and the catalytic layer 4. Namely, flooding can be prevented. As a result, it is possible to increase an area in the fuel cell 100, where a reaction actually occurs, and therefore improve a power density of the fuel cell 100. [0024] As described above, part of the gas in the supply gas passages 6a and part of the gas in the supply gas passage 7a move to the discharge gas passages 6b and 7b through the ribs 2R of the porous bodies 2, respectively, without moving through the diffusion layers 3. Accordingly, it is possible to maintain the electrolyte membrane 5 in an appropriately humid state. Usually, the gas flowing through the supply gas passage 6a and the gas flowing through the supply gas passage 7a, for example, hydrogen and oxygen, are dry. Accordingly, if the ribs 2R of the porous body 2 are not formed, the entire dry gas moves to the discharge gas passages 6b and 7b through the diffusion layers 3. As a result, the electrolyte membrane 5 becomes excessively dry, and the efficiency of electric power generation is reduced. However, in the embodiment, as described above, the ribs 2R of the porous body 2 are formed, and part of the dry gas moves to the discharge gas passages 6b and 7b through the porous bodies 2, without moving through the diffusion layers 3. Accordingly, it is possible to prevent the electrolyte membrane 5 from being excessively dry. [0025] FIG. 3 is a plan view showing the porous body 2 and the gas passages viewed from the direction indicated by an arrow A2 in FIG. 1. For convenience of illustration, FIG. 3 shows the hydrogen gas passage 6a on the anode side and the oxygen gas passage 7b on the cathode side, which are overlapped with each other when seen from the above. Also, FIG. 3 shows the hydrogen gas passage 6b on the anode side and the oxygen gas passage 7a on the cathode side, which are overlapped with each other when seen from the above. Each solid arrow 15 shows a flow of the hydrogen on the anode side, and each dashed arrow 16 shows a flow of the oxygen on the cathode side. Also, as shown by solid arrows in a range A3, the hydrogen on the anode side moves from the supply gas passages 6a to the discharge gas passages 6b. Also, as shown by dashed arrows in the range A3, the oxygen on the cathode side moves from the supply gas passages 7a to the discharge gas passages 7b. [0026] In the embodiment, as shown in each region 2b indicated by a dashed line, the porous bodies 2 are connected to each other at an end portion of each gas passage, whereby each gas passage is formed as a closed passage. Forming each gas passage as a closed passage permits a larger amount of gas to move to the diffusion layer 3. [0027] In addition, in the embodiment, as shown in FIG. 3, the two gas passages are formed so as to be opposite to each other with the diffusion layers 3, the catalytic layers 4, and the electrolyte membrane 5 interposed therebetween, and the direction in which the gas flows in one of the two passages is opposite to the direction in which the gas flows in the other passage. More particularly, an inlet of the hydrogen gas passage 6 on the anode side is opposite to an outlet of the oxygen gas passage 7 on the cathode side. Also, an outlet of the hydrogen gas passage 6 on the anode side is opposite to an inlet of the oxygen gas passage 7 on the cathode side. Usually, the hydrogen and oxygen in the gas passages become drier toward the upstream side in the gas flow, and become more humid due to, for example, generated water toward the downstream side in the gas flow. Accordingly, an upstream portion of the hydrogen gas passage and a downstream portion of the oxygen gas passage are made opposite to each other, and a downstream portion of the hydrogen gas passage and an upstream portion of the oxygen gas passage are made opposite to each other, whereby the porous body 2, the electrolyte membrane 5 and the like located near the inlet of one of the gas passages, which are likely to be excessively dry, can be humidified by the water, for example, generated water existing near the outlet of the other gas passage. It is therefore possible to prevent drying-out that reduces the electric power generation performance of the fuel cell 100. [0028] FIG. 4 is a cross sectional view of the diffusion layer 3 and the porous body 2 taken along a surface perpendicular to the direction in which the gas passages extend. As shown in FIG. 4, the number of holes 11 in the porous body 2 is made larger than the number of holes 12 in the diffusion layer 3. Preferably, the porosity of the porous body 2 is made higher than the porosity of the diffusion layer 3. It is therefore possible to make the gas permeation resistance of the porous body 2 lower than the gas diffusion resistance of the diffusion layer 3. Accordingly, the reaction gas can move sufficiently from the supply gas passages 6a and 7a to the discharge gas passages 6b and 7b, respectively. As a result, it is possible to increase the amount of water to be absorbed in the porous bodies 2. [0029] FIG. 5 is a cross sectional view showing the porous body 2 with the supply gas passage 6a or 7a formed therein, this cross sectional view being taken along a surface parallel to the direction in which the gas flows. As shown in FIG. 5, preferably, the porous body 2 with the supply gas passage 6a or 7a formed therein is configured such that the porosity thereof increases toward the downstream side in the gas flow. Namely, the gas permeation resistance of the porous body 2 positioned on the downstream side is made lower than the gas permeation resistance of the porous body 2 positioned on the upstream side. Accordingly, the generated water, which is likely to be accumulated in a downstream portion of the gas passage as compared to in an upstream portion, can be reliably absorbed in the porous body 2, and therefore the generated water can be discharged effectively. Due to the same reason, preferably, the porous body 2 with the discharge gas passage 6b or 7b formed therein is configured such that the porosity thereof increases toward the downstream side in the gas flow. [0030] In addition, preferably, the water repellency of the porous body 2 is made lower than the water repellency of the diffusion layer 3. Therefore, the generated water can be discharged to the discharge gas passages 6b and 7b further efficiently. [0031] In the invention, the structures and shapes of the separator 1 and the porous body 2 are not limited to the above-mentioned structures and the shapes. In the above- mentioned example, the separator 1 and the porous body 2 are formed of different elements. However, only the separator 1 may be used without using the porous body 2. In this case, the gas passages are formed in the separator 1 , and the separator 1 is formed such that the members between the gas passages are porous. [0032] FIG 6 shows a cell 51 to which a structure of the separator 1 and the porous body 2 according to a first modified example is applied. In the cell 51 according to the first modified example, the porous body 2 is not provided above the gas passages 6a, 6b, 7a and 7b, and only the portions between the gas passages are formed of the porous body 2. With this structure as well, part of the gas in the supply gas passage 6a can permeate through the porous body 2 and move to the discharge gas passage 6b. Similarly, part of the gas in the gas passage 7a can permeate through the porous body 2 and move to the discharge gas passage 7b. Thus, the water existing in the diffusion layer 3 and the catalytic layer 4 can be absorbed in the porous body 2 on each of the anode side and the cathode side. In this case, multiple bar-like porous bodies 2 need to be prepared, instead of forming ribs on the flat porous body 2. Accordingly, the porous body 2 can be prepared easily. [0033] FIG 7 shows a cell 52 to which a structure of the separator 1 and the porous body 2 according to a second modified example is applied. In the cell 52 according to the second modified example, the porous body 2 is not used on the anode side (namely, the gas passages are formed in the separator 1 on the anode side), and the porous body 2 is used only on the cathode side. As described above, when the portions between the gas passages on the anode side are formed of the porous body 2, part of the hydrogen gas supplied to the supply gas passage 6a moves to the discharge gas passage 6b through the porous body 2. When the fuel cell includes a gas passage system of a hydrogen circulation type, the unreacted hydrogen moved to the discharge gas passage 6b returns to the supply gas passage 6a. Accordingly, the hydrogen gas is hardly wasted. However, when a gas passage system of a hydrogen non-circulation type is used, in which the hydrogen gas is discharged from the discharge gas passage 6b as it is, a discharge amount of the hydrogen gas, which does not contribute to the electric power generation due to a reaction in the electrolyte, may increase, and waste of fuel may occur. Therefore, in the second modified example, the porous body 2 is not used on the anode side where hydrogen serving as fuel flows through the gas passages. Namely, a nonporous material is used for forming the portion in which the passages are formed on the anode side. Water is generated mainly on the cathode side. Therefore, even if the porous body 2 is used only on the cathode side, the above-mentioned effect of discharging the generated water can be sufficiently obtained. When a control system of the fuel cell is a hydrogen non- circulation type, the fuel cell formed of the cells 52 according to the second modified example is effective at ensuring the efficient use of hydrogen. [0034] Due to the same reason as the second modified example, the porous body 2, whose porosity is lower than the porosity of the porous body 2 used on the cathode side, may be used on the anode side. Namely, instead of forming the passages on the anode side only in the separator 1 , the porous body, whose porosity is lower than the porosity of the porous body 2 used on the cathode side, may be used for forming the portion in which the passages are formed. It is thus possible to discharge the generated water on the anode side which has been diffused backward from the cathode side through the catalytic layer and the like, while suppressing unnecessary discharge of the hydrogen on the anode side. [0035] [Details of the Embodiment] Hereafter, the fuel cell according to the above-mentioned embodiment will be described in detail. [0036] As shown in FIG. 1, the fuel cell (cell) according to the embodiment includes the separators 1 , the porous bodies 2, the diffusion layers 3, the catalytic layers 4, the electrolyte membrane 5, the supply gas passages 6a and 7a, and the discharge gas passages 6b and 7b. [0037] A perfluoro sulfonic acid ion exchange membrane is used as the electrolyte membrane 5. Then, the electrolyte membrane 5 is coated with a solution containing platinum supporting carbon and an electrolyte, whereby the catalytic layer 4 is formed on the electrolyte membrane 5. As a base material of the diffusion layer 3, porous carbon paper or porous carbon cloth is used. Then, the base material is immersed in a solution containing powder of carbon and PTFE (polytetrafluoro-ethylene), whereby the base material is impregnated and coated with the carbon and the PTFE. Then, the base material coated with the carbon and the PTFE is baked, whereby the diffusion layer 3 is formed. Then, the diffusion layer 3 is overlaid with the catalytic layer 4 formed on the electrolyte membrane 5, and hot press is performed to join the diffusion later 3, the catalytic layer 4 and the electrolyte membrane 5 to each other, whereby the electrode is formed. [0038] A dense carbon plate or a metal plate (e.g., a stainless plate, a titanium plate, and a nickel alloy plate) is used as the separator 1. When a metal plate is used, in order to prevent an increase in contact resistance due to formation of an oxide film on the surface of the separator 1, a surface treatment, for example, an Au coating is applied to the surface of the separator 1 so as to reduce contact resistance. In addition, an anti-corrosion coating is applied to the surface of the separator 1 , when a metal plate is used. For example, a carbon coating is performed by applying a coating formed of a mixture of carbon powder and a binder, for example, rubber to the surface of the separator 1. [0039] The porous body 2 is made of a carbon material (e.g., porous carbon and sintered carbon), as in the case of the diffusion layer 3. The porous body 2 is formed of a carbon whose porosity (for example, 50 % to 80 % in a non-humidified condition, and 40 % to 80% when the pressure applied to the rib surface per a unit area is 1 Mpa) is higher than the porosity of the diffusion layer 3 (for example, 40 % to 70 % in the non-humidified condition, and 30 % to 60 % when the pressure applied to the rib surface per the unit area is 1 Mpa). The ribs are formed on the thus prepared porous body 2, whereby the gas passages 6 and 7 are formed. The gas passages 6 and 7 are formed as closed passages which are not communicated with each other. Each gas passage has a groove width of 0.8 mm, and a groove depth of 0.5 mm. Each rib has a width of 0.8 mm, and a height of 0.5 mm. [0040] As shown in FIG. 3, the porous bodies 2 are provided on the electrodes such that the hydrogen gas passages 6 are opposite to the air gas passages 7. In addition, the separators 1 are provided on the porous bodies 2. Then, sealing is provided to the outer surfaces of the stack using an adhesive seal or a gasket, whereby the fuel cell (cell) is formed. [0041] FIG. 8 shows the result of comparison of cell performance between the fuel cell formed in the above-mentioned manner and fuel cells in which the porous body 2 is not used. In FIG. 8, the horizontal axis shows a current density (A/cm²), and the vertical axis shows a cell voltage (V). Namely, FIG. 8 shows the current-voltage characteristics (cell characteristics) of these fuel cells. A curve Bl shows a current-voltage characteristic of a fuel cell in which the porous body 2 is not used, and the closed passages are not applied to the passages (namely, straight passages are used) (comparative example 1). A curve B2 shows a current-voltage characteristic of a fuel cell in which the porous body 2 is not used and closed passages are applied to the passages (comparative example 2). A curve B3 shows a current-voltage characteristic of the fuel cell according to the embodiment in which the porous body 2 is used and the closed passages are applied to the passages. [0042] It can be understood from FIG. 8 that, in a region in the graph, in which the current density is high, the voltage of the fuel cell according to the embodiment drops more gradually than the voltage of each of the fuel cells according to the comparative examples 1 and 2 drops. Namely, it can be understood from FIG. 8 that the cell performance of the fuel cell according to the embodiment is higher than the cell performance of each of the fuel cells according to the comparative examples 1 and 2. The result shows that the gas diffusion region is increased and the generated water can be discharged further efficiently by employing the porous body 2 and the closed passages in the fuel cell, whereby the area in which the reaction actually occurs is increased and therefore the cell performance is improved.

Claims

CLAIMS:

1. A fuel cell in which communication is not permitted between a supply gas passage and a discharge gas passage that are formed in a separator provided on an electrode, wherein a member of the separator, which forms a portion between the supply gas passage and the discharge gas passage is porous.

2. The fuel cell according to claim 1 , wherein a diffusion layer of the electrode is porous, and a porosity of the member is higher than a porosity of the diffusion layer.

3. The fuel cell according to claim 1 or 2, wherein the member is configured such that the porosity of the member increases toward a downstream side in a gas flow.

4. The fuel cell according to any one of claims 1 to 3, wherein the member is provided in only the separator on a cathode side of the fuel cell.

5. The fuel cell according to any one of claims 1 to 3, wherein the porosity of the member on a cathode side is higher than the porosity of the member on an anode side.

6. The fuel cell according to any one of claims 1 to 5, wherein water repellency of the member is higher than water repellency of the diffusion layer.

7. A separator for a fuel cell, in which a supply gas passage and a discharge gas passage are formed such that communication between the supply gas passage and the discharge gas passage is not permitted, wherein a member of the separator, which forms a portion between the supply gas passage and the discharge gas passage is porous.

8. A fuel cell, comprising: an anode; a cathode; an electrolyte membrane which is inteφosed between the anode and the cathode; a first separator including a first separator main body, and a first member which is provided between a first supply gas passage that supplies fuel gas to the anode and a first discharge gas passage that discharges the fuel gas from the anode such that communication between the first supply gas passage and the first discharge gas passage is not permitted; and a second separator including a second separator main body and a second member which is provided between a second supply gas passage that supplies oxidizing gas to the cathode and a second discharge gas passage that discharges the oxidizing gas from the cathode such that communication between the second supply gas passage and the second discharge gas passage is not permitted, wherein at least one of the first member and the second member is porous.